1. Field of the Invention
The present invention relates to the field of dental radiography; and more particularly to means for establishing a constant exposure orientation, and positively identifying viewing orientation of dental film and copies made thereof.
2. Description of the Prior Art
A dental radiograph is an x-ray image of one or more teeth and surrounding bone that is achieved by placing an x-ray film, enclosed in a light-proof package, into the mouth, on one side of a dental structure, while an x-ray tube is aimed at the film from the other side of the structure, generally from outside the face. After the film is developed, it is customarily mounted in a frame of cardboard or plastic for viewing and storage. The mounting of dental radiographs for viewing can be a complex process and has been likened to solving a jigsaw puzzle, requiring a working knowledge of dental anatomy and facial osteology. Since adjacent teeth, opposing teeth, and teeth in the opposite side of the mouth may all appear similar to one another and since the mounting is often performed by technical personnel of varying degrees of training and experience, errors inevitably occur. If an error is made and escapes detection it can lead to treatment of the wrong tooth.
The film is conventionally provided with a "button" along one edge. This button consists of a depression created in one surface of the film and a corresponding raised bump in the opposite surface. The raised side normally corresponds to the side of the film that faced the x-ray tube during exposure. Because of its large size relative to the structures being imaged, this button can cause unacceptable distortion of the underlying image. It is therefore recommended in the literature, as in "Dental Radiology" by Wuehrmann et al., that the button be positioned toward the occlusal plane so as not to superimpose on important dental structures.
While the button is intended to identify the exposure side of the film, it has several disadvantages. First, the button measures approximately 2 mm in diameter and over 3 square millimeters in area, and its curved surface results in distortion of the underlying image. It is therefore positioned close to the edge of the film to prevent it from superimposing on important structures, and it is thus frequently not visible on the mounted film, being partially or completely covered by the mounting frame. The viewer of the mounted film cannot then readily determine whether the film has been properly mounted without removing the film from the frame. Second, when copies are made of the original radiograph, an increasingly common practice because of the rise in dental consultation and litigation, the button is not consistently visible on such copies. The dentist receiving such copies is deprived of the orientation information provided by the original film and may need to repeat the radiographs if there is a question of incorrect mounting. The film manufacturer normally impresses letters or symbols along one edge of the film for manufacturer's identification but these impressions, like the button, are normally hidden by the mounting frame and are not consistently visible on radiographic copies. Furthermore, there are times when the dentist or his personnel may need to determine whether the film they are viewing is an original or a duplicate, for example when films need to be sent out and they wish to be sure to retain the originals for legal considerations. Despite certain differences discernible on careful scrutiny of the two types of films, confusion sometimes arises in telling one from another. It is desirable for office personnel to be able to easily distinguish one film type from another.
French patent 2,618,917 to Zabiolle discloses a method of engraving an inscription on a plate that is attached to a dental x-ray film during exposure to mark the film with the inscription. Canadian patent 1,249,745 to Tanaka discloses an information bearing sheet for x-ray film made of paper or plastic with identification numbers printed in ink containing lead. The need remains in the art for a method and means capable of modifying x-ray dental film to: (1) establish a constant exposure orientation; and (2) positively identify the viewing orientation of the film and copies made thereof.